Firing with such a fire arm requires that the shooter holds the fire arm in a correct elevation angle, as a function of the distance of the target, for the projectile to effectively reach the latter during its ballistic trajectory. While doing so, the shooter must also preserve the right azimuth of alignment with regard to the target, while moving the fire arm to give it the right elevation.
Mechanical sighting systems exist, such as described in U.S. Pat. Nos. 6,568,118 and 3,604,137, which enable the shooter, as soon as he has estimated at what distance the target is situated or has obtained the exact distance by means of a range finder, to manually align the sighting element at the correct angle, given for example by an angular scale.
Such mechanical systems have two major disadvantages:                the time to take aim is extended, as the shooter must first adjust the sighting element in a mechanical manner,        while adjusting the range finder, the shooter loses track of the target.        
More sophisticated sighting systems exist as well, as the one described in patent EP 0 785 406, which provide, in an optical window or on a video screen, the image of a reticle that moves automatically as a function of the measured distance, whereby the shooter must align said image with the target.
Such solutions including systems with what are called a “moving red point” in which the image of the reticle is projected to infinity at the correct angle, so as to eliminate the parallax error, are disadvantageous in that they are too heavy and too sizeable to be used for example on an assault gun.